Nanocrystalline cellulose (NCC) isolation from non-woody biomass is attractive to replace the current reliance on wood as feedstock. The predominant use of single acid hydrolysis cycle in existing literature may overlook the residual sediment. In this work, we explored the use of multiple acid hydrolysis to investigate the NCC isolation from unbleached kapok pulp. Initial screening using factorial design showed the significance of acid concentration, reaction time and temperature as crucial variables in determining the NCC characteristics, among five variables examined which also included sonication time and acid-to-pulp ratio. Subsequent optimisation using central composite design demonstrated that the optimal reaction condition for NCC recovered from supernatants entails a single cycle employing 63%w/w of sulphuric acid at 45 °C for 50 min with acid-to-pulp ratio of 30:1 mL/g and sonication time of 5 min. The NCC yield obtained (supernatant) was ∼19 % with PDI of 0.4, zeta potential of −39.7 mV and crystallinity index of 72.6 %. When combining with the further hydrolysis of sediments, the data showed comparable responses for NCC produced (yield, size and zeta potential) using either 3 cycles or 1 cycle. Nevertheless, opting for 3 cycles resulted in a lighter NCC colour owing to lower acid concentration and temperature. This study demonstrated that the feasibility of adjusting the number of hydrolysis cycles based on the desired outcome for NCC isolation.

中文翻译：

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通过多次酸水解从未漂白的木棉籽荚纤维生产纳米晶纤维素：“多即是少”还是“少即是多”？


从非木质生物质中分离纳米晶纤维素（NCC）对于取代目前对木材作为原料的依赖具有吸引力。现有文献中主要使用单一酸水解循环可能会忽略残留沉积物。在这项工作中，我们探索了使用多重酸水解来研究未漂白木棉浆中 NCC 的分离。使用因子设计进行的初步筛选表明，在检查的五个变量中，酸浓度、反应时间和温度作为确定 NCC 特性的关键变量具有重要意义，其中还包括超声处理时间和酸浆比。使用中心复合设计的后续优化表明，从上清液中回收 NCC 的最佳反应条件需要在 45 °C 下使用 63%w/w 硫酸进行单循环 50 分钟，酸浆比为 30:1 mL/ g，超声处理时间 5 分钟。获得的 NCC 产率（上清液）约为 19%，PDI 为 0.4，zeta 电位为 -39.7 mV，结晶度指数为 72.6%。当与沉积物的进一步水解相结合时，数据显示使用 3 个循环或 1 个循环产生的 NCC 的类似响应（产量、尺寸和 zeta 电位）。然而，由于酸浓度和温度较低，选择 3 个循环会导致 NCC 颜色变浅。这项研究证明了根据 NCC 分离的预期结果调整水解循环次数的可行性。